Environmental concerns have led to continued efforts to reduce the CO, hydrocarbon and nitrogen oxide (NOx) emissions of compression ignited (diesel-fueled) and spark ignited (gasoline-fueled) light duty internal combustion engines. Further, there have been continued efforts to reduce the particulate emissions of compression ignited internal combustion engines. To meet the upcoming emission standards for heavy duty diesel vehicles, original equipment manufacturers (OEMs) will rely on the use of additional exhaust gas after-treatment devices. Such exhaust gas after-treatment devices may include catalytic converters, which can contain one or more oxidation catalysts, NOx storage catalysts, and/or NH3 reduction catalysts; and/or a particulate trap.
Oxidation catalysts can become poisoned and rendered less effective by exposure to certain elements/compounds present in engine exhaust gasses, particularly by exposure to phosphorus and phosphorus compounds introduced into the exhaust gas by the degradation of phosphorus-containing lubricating oil additives. Reduction catalysts are sensitive to sulfur and sulfur compounds in the engine exhaust gas introduced by the degradation of both the base oil used to blend the lubricant, and sulfur-containing lubricating oil additives. Particulate traps can become blocked by metallic ash, which is a product of degraded metal-containing lubricating oil additives.
To insure a long service life, lubricating oil additives that exert a minimum negative impact on such after-treatment devices must be identified, and OEM specifications for “new service fill” and “first fill” heavy duty diesel (HDD) lubricants require maximum sulfur levels of 0.4 mass %; maximum phosphorus levels of 0.12 mass %, and sulfated ash contents below 1.1 mass %, which lubricants are referred to as “mid-SAPS” lubricants (where “SAPS” is an acronym for “Sulfated Ash, Phosphorus, Sulfur”). In the future, OEMs may further restrict these levels maximum levels to 0.08 mass % phosphorus, 0.2 mass % sulfur and 0.8 mass % sulfated ash, with such lubricants being referred to as “low-SAPS” lubricating oil compositions.
As the amounts of phosphorus, sulfur and ash-containing lubricant additives are being reduced to provide mid- and low-SAPS lubricants that are compatible with exhaust gas after-treatment devices, the lubricating oil composition must continue to provide the high levels of lubricant performance, including adequate detergency, dictated by the “new service”, and “first fill” specifications of the OEM's, such as the ACEA E6 and MB p228.51 (European) and API CI-4+ and API CJ-4 (U.S.) specifications for heavy duty engine lubricants. Criteria for being classified as a lubricating oil composition meeting the above listed industry standards is known to those skilled in the art.
The ability of a lubricant to neutralized acidic byproducts of combustion, which increases in engines provided with exhaust gas recirculation (EGR) systems, particularly condensed EGR systems in which exhaust gasses are cooled prior to recirculation, can be improved, and the drain interval of the lubricant can be extended, by increasing the total base number (TBN) of the composition. Historically, TBN has been provided by overbased detergents that introduce sulfated ash into the composition. It would be advantageous to provide a lubricating oil composition with a high level of TBN using a TBN boosting component that does not contribute sulfated ash. As highly basic components are known to induce corrosion and, in some cases reduce the compatibility between lubricating oil compositions and the fluoroelastomeric seal materials used in engines, it would be preferable to provide such a component that does not induce corrosion and, preferably, does not adversely affect seals compatibility. Due to demands for improved fuel economy, less viscous lubricants, such as 0 W and 5 W 20 and 30 grade lubricants have become more prevalent. To allow for easier formulation of such lubricants, the amount of polymer introduced by additives is preferably minimized. Therefore, it would be further preferable to provide a non-polymeric ashless TBN source.
U.S. Pat. Nos. 5,525,247; 5,672,570; and 6,569,818 are directed to “low ash” lubricating oil compositions in which sulfated ash content is reduced by replacing overbased detergents with neutral detergents. These patents describe such lubricants as providing sufficient detergency, but make no claim that such lubricants will provide sufficient TBN for use, for example, in HDD engines. US Patent Application 2007/0203031 describes the use of a high TBN nitrogen-containing dispersants as ashless TBN sources.